Transformers have been popularly used in many electric or power apparatuses to pull up/down voltages or provide impedance matching. Basically, the impedance matching would be adjusted according to equipment requirement (e.g. gain, efficiency, power, signal-to-noise ratio (SNR), etc.). For instance, in order to optimize the power delivered from a signal source to a load circuit, an impedance ratio of the transformer may be adjusted, such that the output impedance of the signal source would match the impedance of the load circuit.
In the field of impedance matching, a lot of techniques have been disclosed. For example, Macphail disclosed “Switched impedance transformer for semiconductor circuits” in U.S. Pat. No. 7,616,934. Lee et al. disclosed “Systems and methods for a SPDT switch or SPMT switch with transformer” in U.S. Pat. No. 8,044,540.